Solid ink or phase change ink printers conventionally receive ink in a solid form, either as pellets or as ink sticks. The solid ink pellets or ink sticks are placed in a feed chute and a feed mechanism operates to deliver the solid ink, hereafter may be referred to as sticks or ink, though a feed chute to a heater assembly. The feed mechanism may be configured to use gravity or a mechanical bias to urge the ink through the feed chute so they impinge upon a heater plate in the heater assembly. The heater plate melts the solid ink impinging on the plate into liquid ink that is collected and delivered to a print head for jetting onto a recording medium. U.S. Pat. No. 5,734,402 for a Solid Ink Feed System, issued Mar. 31, 1998 to Rousseau et al.; and U.S. Pat. No. 5,861,903 for an Ink Feed System, issued Jan. 19, 1999 to Crawford et al. describe exemplary systems for delivering solid ink sticks into a phase change ink printer.
Phase change or solid inks for color printing typically comprise an ink carrier composition that is combined with compatible colorants. In a specific embodiment, a series of colored inks can be formed by combining ink carrier compositions with compatible colorants. The resulting subtractive solid ink primary-colors may be melted to yield the typical color set, namely, cyan, magenta, yellow and black, although other colors may be produced.
Ink sticks historically in use are manufactured with a formed tub and flow fill process. In this method, the ink compound is poured into a tub having an interior shape corresponding to the desired finished ink stick shape. The tub may also be formed with indentations and protrusions for forming keying and coding features in the ink sticks, if desired. This manufacturing method allows formation of ink sticks with inset features and contours at the bottom and sides of the stick, but may produce a stick periphery with imprecise tolerance control and limited complexity. Sharply defined features and undercut features that are transverse to the removal direction of the ink sticks from the tubs are difficult to preserve during extraction of a stick.
This method is also ineffective for controlling height or forming features in the upper surface of a stick. Because the top of the forming tub remains open during the process, the top surface of the ink material may solidify without uniformity. Liquid ink shrinks in volume as it cools and this size change deforms the ink and generates stress. Non uniform cooling exacerbates this tendency. Consequently, the top surface may include cracks and congeal with an irregular shape. These irregularities may result in handling fragility. In some instances, the height variation may be significant enough to adversely affect loading and transport of the stick.
Pour molding may be used with molding tools instead of a tub as described above. Typical molding tools are generally rigid and made from a heat tolerant, machinable material, such as aluminum or steel. The physical properties of the ink material, which is intended to adhere to media such as paper and transparencies, may cause the ink to adhere to the cavity of a typical molding tool. The wax-like nature of the ink material may be difficult to eject from the tool. Small volumes of ink can be torn away from the ink stick body and remain in the tool following ink stick extraction. Long cool down periods and/or low friction release coatings, such as, for example, polytetrafluoroethylene (PTFE), may help reduce the likelihood of ink sticking to a tool. Release coatings add cost, gradually deteriorate and do not solve stick geometry limitation problems.